Was it while reviewing the pictures after shooting? And if so, was it only the bright areas of the photograph flashing from white to black? If that is the case, then you'll have your camera's playback mode on "Highlights". Press down or up on the D-pad until you can see the a time, date, and your image's filename.

If it isn't that, however, then we'll need some pics to determine what's up.

bear in mind that the highlight warning is there to let you know if you've lost detail in some areas of the photo. So turning it off just hides the problem. It's better to adjust your exposure to avoid it. Exposure compensation can help with this.